Abstract

A half joint is a particular type of RC structure. Within the existing UK Highways Agency network alone there are 400+ concrete bridges with half joints. The advantages of this structural form include a level running surface along the bridge deck and the support spans, and precast beams can be easily lifted into place and supported during construction. However, a disadvantage inherent in this type of construction is that there are problems associated with leakage through the joint. This enables moisture to accumulate at the beam seats thereby increasing the propensity for the deterioration of the concrete and reinforcement steel. The situation is adversely compounded by limited access to the bearing seat joint which leads to both inspection and maintenance issues. A further complication is that the detail in the beam seat region represents a potentially sensitive structural detail. Some half-joint structural vulnerabilities may have been present from the outset e.g. in the initial design or construction, some may develop with time e.g. deterioration. Half joint details have come under intense scrutiny since the collapse of a section of the de la Concorde Overpass in Quebec, Canada in 2006. Five people were killed and six others injured. Thus, a key challenge is to understand the lessons to be learned from the Concorde Overpass Collapse, and the inherent vulnerabilities in half joint structures.This project will provide improved analytical tools and experimental evidence for the more accurate assessment of half-joint structures, and will inform the management strategy for half-joint structures throughout the UK. Overly conservative strength assessments can result in unnecessary closures or vehicle weight limits, both of which are costly. Non-conservative strength assessments potentially put public safety at risk. The outcomes of this project are therefore of national, and international importance.The behaviour of reinforced concrete structures in shear is notoriously complex and there is no generally accepted unifying theory. This presents a major difficulty in the analysis of half-joint structures. The current work will explore, compare, extend, and adapt existing theories in the context of half-joint structures. A further goal is to incorporate detailing deficiencies and/or deterioration within the analytical and experimental approaches to thereby enhance the predictive capability for structures in service. The load-sharing implications in non-compliant details and the sensitivity of the structural performance to a deterioration outcome, such as a loss of strength will be investigated. This approach reflects the type of information that would be collated as part of a destructive or non-destructive testing strategy, and provides a general, robust and repeatable framework from which others can benchmark their results. Experiments on small and large scale specimens will be undertaken to provide the essential validation of the expected behavior. Small-scale tests will be used to characterise the bond anchorage behaviour in a representation of a deteriorated system. The large-scale tests will deliver an experimental database of half-joint structures with non-compliant details and determine the influence of strength reductions in the constituent materials. This will provide an important experimental evidence of the behavior of such structures, and highlight the most critical detailing and deterioration combinations. While the project has been inspired by, and will address, the difficult challenges faced by those who build, own and maintain reinforced concrete bridges, the development of the underlying fundamental scientific and engineering understanding will have far greater implications. A fuller understanding of the failure modes and sensitivities associated with complex reinforced concrete details will provide insight into the life-time performance of a wide range of existing infrastructure assets.

Planned Impact

After the tragic collapse of the Concorde Overpass in Quebec, Canada, the appointed Commission of Inquiry made a number of recommendations for future practice including the need to 'Improve the knowledge acquisition process'. In particular, the Commission recommended that [1]' ... the Government ensure that there be an effective surveillance of scientific intelligence processes and knowledge involving academics and top-level practitioners; this will ensure that persons responsible for designing and maintaining structures, both in private practice and in Government services, be kept constantly informed of new developments and changes in standards and practices.' Although this statement was in a Canadian context, the message resonates globally. The project team assembled to deliver the proposed work includes international and national representation, private and public organizations, and academic and industrial partners. This combination of expertise will present a powerful mechanism in which to improve the knowledge acquisition process both within, and beyond the UK sector.The academic merit will be of interest to researchers and practitioners across a range of disciplines including structural engineers, material scientists and analytical modelers. The developed tool(s) with which to assess half joint structures will provide invaluable information about the sensitivities within a given structure to detailing deficiencies and/or deterioration. The undertaking of novel experiments will provide an experimental database of non-compliant half-joint structures, provide an important experimental basis for the effects of a strength loss in the constituent materials (as a representation of deterioration), and highlight the most critical combinations. The outcomes will contribute towards the formulation of informed, evidence-based policy approaches for the assessment and monitoring of the UK's 400+ half joint structures. Most importantly, the research will also be applicable more broadly in the context of the determination of the residual strength capacity of existing reinforced concrete infrastructure.The dissemination of the results through undergraduate and graduate teaching programmes will improve the awareness of future generations of engineers to the complexities hidden within our surrounding built environment and the urgent need for validated strategies, with a sound theoretical foundation, to assist with the ongoing challenges associated with an aging infrastructure asset profile. The skills gained by the post-doc working on the project will result in a range of advanced analytical and experimental expertise, the outcome of which will be a highly employable individual with a bright academic, or non-academic professional future.

[1] Commission of Enquiry into the collapse of a portion of de la Concorde Overpass, Government of Quebec, 2007.

The research has led to an enhanced fundamental understanding of the impact of design choices, deterioration mechanisms and synergistic effects on the load carrying capacity of existing reinforced concrete half-joints. A reinforced concrete half-joint beam has a complex geometry that includes both a locally disturbed nib region and a full depth section. While this configuration simplifies the design and construction procedures, half joint structures rely on the internal steel reinforcement to transfer force from the nib into the bulk of the beam. To provide a better understanding of the contribution of selected internal steel reinforcing bars, the impact of local corrosion, anchorage cracking, limited amounts of shear reinforcement, and improper reinforcement detailing, an experimental test program on full-scale half-joint beams was undertaken. The results indicated that if certain bars are missing the overall load bearing capacity of a half-joint could be approximately 40% lower than that of a properly designed detail, but that a redistribution of forces was noted. It was also found that when multiple deterioration processes are noted and/or questions are raised with respect to the reinforcement detailing, the impact on the load carrying capacity of the beam can be larger than the linear combination of the individual effects. So although the impact of an individual shortcoming on the load carrying capacity of reinforced concrete half-joint beams might not be substantial, inspectors and assessors should pay particular attention to the possibility of combined effects. The experimental results were compared with predictions using different strut-and-tie models (STMs) and the applicability of STMs to achieve the highest lower bound estimate of the load carrying capacity was investigated. For the beams studied in the current work, the predictions based on codes and standards, combined with appropriate methods to incorporate deterioration effects, led to safe load bearing capacity estimates. However, the developed STMs seem to be, in some instances, unable to pick up alternative load paths that develop as soon as the capacity of a certain tie is reached. Hence the actual load capacities might be higher than what is obtained from the STM calculations. A further discovery was in connection with the influence of cracking on the bond behaviour of internal reinforcing steel. Cracks are inherent in reinforced concrete half-joint structures, due to the relatively low tensile strength of concrete. A common cause of cracking is the corrosion of internal steel reinforcement, a deterioration process that can affect the bond behaviour and anchorage capacity of reinforcing bars. Corrosion leads to a reduction of the reinforcing bar diameter, the formation of a weak layer of corrosion products around the bar and expansive forces on the surrounding concrete. The more fundamental impact of cracking as distinct from corrosion products on the bond reduction is still not fully understood. A novel test method to investigate the bond behaviour of reinforcing bars in cylindrical cracked reinforced concrete specimens was developed. The influence of the number of cracks, crack orientation, confinement and concrete cover were investigated. The results indicate a significant loss of bond strength for single cracked specimens. This reduction becomes as high as 65% for double cracked specimens in the absence of confinement. It was shown that the crack orientation with respect to the rib pattern is of minor influence, but the concrete cover and confinement play a significant role in the obtained bond characteristics.

Exploitation Route

The results of this project are being taken forward by Highways England (in collaboration with the team at the University of Cambridge) to develop and update existing half-joint bridge assessment guidelines. They will form part of the necessary underpinning evidence for adjusted methodologies and calculation approaches. This should lead to a more reliable assessment of deteriorating half-joints and a better use of limited resources when it comes to the renovation, strengthening and/or replacement of reinforced concrete half-joints. A number of research publications have been published to disseminate the work to academic audiences and practicing engineers. The success of the project led to a University of Cambridge EPSRC Impact Acceleration Account award to strengthen the Cambridge/Highways England (HE) alliance. This has led to the submission of joint Cambridge/HE publications for improved approaches for the management and assessment of reinforced concrete half joints.

Sectors

Construction,Transport

Description

Our research is informing strategies for the assessment of existing half-joint infrastructure.

Knowledge transfer, incorporation of research findings into design guidance and Industry practice

Start Year

2013

Description

Highways Agency

Organisation

Department of Transport

Department

Highways Agency

Country

United Kingdom

Sector

Public

PI Contribution

Knowledge transfer, delivery of research advances and sharing of research findings

Collaborator Contribution

The Highways Agency have supported a number of funded EPSRC projects including (EP/K016148, GR/S55101/01, EP/I018972/1 and EP/J002887/1). This support has included technical guidance, access to data relating to reinforced concrete infrastructure, sharing of experience in managing the strategic road network in the UK and guidance regarding the main challenges faced on the network. This has ensured the long-term relevance of our research and extensive knowledge exchange.

Knowledge exchange between the University of Cambridge and McGill University

Organisation

McGill University

Country

Canada

Sector

Academic/University

PI Contribution

Knowledge transfer, exchange of recent research findings

Collaborator Contribution

Professor Mitchell is an expert on the behaviour of reinforced concrete half joints and collaborated with Cambridge on grant EP/K016148/1. He has conducted experimental and analytical investigations of reinforced concrete half joints and served as an expert to the Canadian Commission of Inquiry into the collapse of a section of the de la Concorde Overpass.

Impact

Knowledge transfer, technical advice

Start Year

2014

Description

Knowledge exchange between the University of Cambridge and Queen's University

Organisation

Queen's University

Country

Canada

Sector

Academic/University

PI Contribution

As a result of Dr Janet Lees' overseas travel award for research visits to Canada (EP/J002887/1), Dr Lees and Professor Hoult from Queen's University strengthened existing collaborations and forged new collaborations. They collaborated on an MSc student project at Queen's University which was based on research conducted at Cambridge investigating crack propagation. This resulted in a joint publication. Dr Lees has provided strategic technical guidance through her membership of the Steering Committee of a Canadian NSERC Strategic grant led by Professor Hoult in collaboration with the University of Toronto and the University of Ottawa.

Collaborator Contribution

Professor Hoult and his team have provided fibre optic sensor and digital image correlation expertise which has helped to validate models developed at Cambridge. Professor Hoult was a member of the International Steering Committee for our Cambridge-based EPSRC funded research project (EP/K016148/1) to investigate reinforced concrete half joints and is collaborating with Professor Lees on EPSRC Established Career Fellowship Tailored Reinforced Concrete Infrastructure project (EP/N017668/1). During regular visits to Cambridge Professor Hoult has been working with the project team on collaborative aspects. We also collaborate through SKYPE meetings.

Impact

Additional research funding, international research collaboration, knowledge transfer, student training

Start Year

2010

Description

Knowledge exchange between the University of Cambridge and University of Toronto

Organisation

University of Toronto

Department

Civil and Mineral Engineering

Country

Canada

Sector

Academic/University

PI Contribution

As a result of Dr Janet Lees' overseas travel award for collaborative research visits to Canada (EP/J002887/1), a number of new and exciting research projects have been instigated in collaboration with the University of Toronto (U of T). A PhD project at the University of Cambridge (2012-2016) undertook research to investigate the time-dependent behaviour of reinforced concrete. The Cambridge PhD student applied an analytical approach developed at the University of Toronto (U of T) and linked this to experiments undertaken in Cambridge. The collaboration with U of T also benefited an EPSRC funded project relating to the CFRP shear strengthening of reinforced concrete T-beams (EP/J002887/1) where the Cambridge team built on analytical work undertaken by the University of Toronto and adapted this to a new class of problems. Our two Institutions actively share and discuss research findings.

Collaborator Contribution

Under the aegis of EP/J002887/1 Professors Bentz and Collins hosted Dr Lees in Toronto during Spring/Summer 2012 and subsequently on short term repeat visits during 2013/2104. Dr Lees worked with Professors Bentz and Collins during her stays and was not charged a bench fee. As a result of these visits and discussions, Dr Lees submitted a successful EPSRC proposal - Reinforced concrete half-joint structures: Structural integrity implications of reinforcement detailing and deterioration (EP/K016148/1). To further develop our collaboration, Professor Bentz spent a three month period of sabbatical leave at the University of Cambridge in 2014. Professors Bentz and Collins were International Collaborators on the EPSRC project on reinforced concrete half-joint structures (EP/K016148/1) and are also collaborating with Cambridge on our latest work on tailored reinforced concrete infrastructure (EP/N017668/1).

Impact

Additional research funding, international research collaboration, new approaches to reinforced concrete design, analysis and assessment, student training

Ongoing engagement with ARUP team regarding research findings
Hosting of a Cambridge/ARUP meeting in Cambridge on Feb 1, 2019 on recent research findings in relation to the strength assessment of reinforced concrete bridges, and tailored reinforced concrete structures

Collaborator Contribution

Technical advice and feedback

Impact

Closer collaboration, knowledge transfer

Start Year

2017

Description

Parsons Brinckerhoff

Organisation

Parsons Brinckerhoff

Country

United States

Sector

Private

PI Contribution

Knowledge transfer, delivery of research advances and sharing of research findings

Collaborator Contribution

Chairing/membership of steering committees for a number of EPSRC funded grants, technical advice and support

Impact

Knowledge transfer, incorporation of research findings into design guidance and Industry practice

One of our former team members (Desnerck) gave a presentation on 'Suggestions for improved reinforced concrete half-joint bridge inspection in England' during 5th International Conference on Concrete Repair, Rehabilitation and Retrofitting, ICCRRR 2018, Cape Town, South Africa. This was a paper co-authored with colleagues at Highways England.

Year(s) Of Engagement Activity

2018

Description

Cambridge/Highways England Roadmapping Workshop

Form Of Engagement Activity

Participation in an activity, workshop or similar

Part Of Official Scheme?

No

Geographic Reach

National

Primary Audience

Professional Practitioners

Results and Impact

This was a high-level workshop facilitated by the Cambridge Institute for Manufacturing Education and Consultancy Services. It drew together professionals from Highways England and researchers from the Concrete and Composites Research Group led by Janet Lees to discuss and formulate fruitful and collaborative research areas and directions .

Year(s) Of Engagement Activity

2017

Description

Development of a Civil Engineering session at ECCM 17

Form Of Engagement Activity

A formal working group, expert panel or dialogue

Part Of Official Scheme?

No

Geographic Reach

International

Primary Audience

Professional Practitioners

Results and Impact

The 17th European Conference on Composite Materials took place in June 2016. Together with Professor Ur Meier (chair) and Guijin Xian, Dr Lees was involved in the initial stages of the development of a session specifically related to Civil Engineering Applications.

Janet Lees gave an invited lecture on 'Engineering in light of great, and unknowable, forces' as part of the inaugural BRE Centre for Innovative Construction Materials lecture series at the University of Bath

Year(s) Of Engagement Activity

2017

Description

Involvement with the work of COST TU1207

Form Of Engagement Activity

A talk or presentation

Part Of Official Scheme?

No

Geographic Reach

International

Primary Audience

Professional Practitioners

Results and Impact

Dr Lees actively participated in the COST TU1207 work. This has included giving presentations, submitting short research contributions and chairing sessions.

The event was held at the National Composites Centre to showcase research and development at a number of UK universities. This led to increased engagement and networking amongst participants. Dr Lees presented an overview of the latest findings from the University of Cambridge.

As a result of the panel sessions, industry partners have engaged and expressed a commitment in supporting research projects related to ultra-high performance fibre reinforced concrete and also the mitigation of the environmental impact of concrete. These will now be developed further in collaboration with the EPSRC IKC Cambridge Centre for Smart Infrastructure & Construction.

Year(s) Of Engagement Activity

2018

Description

Pecha Kucha presentation at Science Festival

Form Of Engagement Activity

A talk or presentation

Part Of Official Scheme?

No

Geographic Reach

Local

Primary Audience

Schools

Results and Impact

One of our research team, Michele Mak, presented a talk at the Cambridge Science Festival - Hidden secrets of concrete bridges - about his research with 20 slides where each slide is shown for 20 seconds.

Presentation by a team member (Mak) on 'Correlation between surface crack width and steel corrosion in reinforced concrete' during 5th International Conference on Concrete Repair, Rehabilitation and Retrofitting, ICCRRR 2018, Cape Town, South Africa

Year(s) Of Engagement Activity

2018

Description

Presentation at the The Hong Kong University of Science and Technology - Lifetime Extension of Reinforced Concrete Infrastructure

Form Of Engagement Activity

A talk or presentation

Part Of Official Scheme?

No

Geographic Reach

International

Primary Audience

Postgraduate students

Results and Impact

An opportunity to share research findings and explore joint interests.

Year(s) Of Engagement Activity

2015

Description

Presentation during International Conference on Concrete Repair, Rehabilitation and Retrofitting

Form Of Engagement Activity

A talk or presentation

Part Of Official Scheme?

No

Geographic Reach

International

Primary Audience

Professional Practitioners

Results and Impact

Presentation "Bond of Reinforcing Bars in Cracked Concrete", during the 2015 International Conference on Concrete Repair, Rehabilitation and Retrofitting, Leipzig, German

The workshop drew together a number of diverse stakeholders from Highways England, Heriot-Watt University, Cambridge University and a representative from one of Highways England's Framework providers to discuss and share the latest findings and developments relating to reinforced concrete half-joint structures.

Year(s) Of Engagement Activity

2017

Data

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